SSD (Solid State Drive) mounting thereon a memory chip comprising NAND type storage cells is paid attention as a memory system used in a computer system. The SSD is advantageous in being faster and lighter in weight than a magnetic disk device.
In recent years, the SSD drives a plurality of memory chips in parallel thereby to enhance a transfer efficiency. One parallel operating method is a technique for interleaving a plurality of memory chips connected to the same channel in units of bank (bank interleaving). With the bank interleaving, a time to transfer data (including command, address, read data and write data) between a data transfer device and the memory chips is concealed by a time taken for the processing inside the memory chips, thereby enhancing a transfer efficiency of the memory system.